Officials cite a possible flaw in the request because the U.S. had failed to turn over certain documents. The director has been released from house arrest.

Reporting from London — Oscar-winning film director Roman Polanski will not be extradited to the United States to face sentencing for having sex with a 13-year-old girl more than 30 years ago, Swiss authorities announced Monday.

The Swiss Federal Department of Justice and Police said a flaw in the U.S. extradition request could not be ruled out and that Polanski, who maintains a vacation home in Switzerland, could reliably expect not to be arrested and deported since the U.S. knew of his frequent presence there over the past few years but never acted on it.

Polanski, 76, has already been released from house arrest, the justice department said.

The announcement was a dramatic development in a case that has lasted more than 30 years. In 1978, Polanski fled the U.S. hours before he was to be sentenced for having unlawful sex with a minor.

He has not set foot in the U.S. since. Born in Poland, Polanski is now a French citizen.

The director has been in Swiss custody since September of last year, when police in Zurich arrested him upon his arrival in the city to accept a lifetime achievement award at the local film festival. The arrest was performed at the request of authorities in Los Angeles.

The U.S. lodged a formal extradition request at the end of October. Legal experts said that, by law, Swiss justice officials were obliged to rule on the request only on technical and administrative grounds, examining it to see that all proper procedures were followed, rather than on the actual merits of the case against Polanski.

In its decision Monday, the Swiss justice department said it could not exclude the possibility that the extradition request was "undermined by a serious fault," because the U.S. had failed to turn over certain documents requested by the Swiss with regard to the case.

Specifically, the Swiss wanted to determine whether the 42 days Polanski already served in a Los Angeles jail would have been considered sufficient time served for having sex with a minor.

Also, Swiss authorities said the U.S. had known since 2006 that Polanski regularly visited Switzerland to stay in his chalet in Gstaad yet did not file any action against him until last year. That gave Polanski a reasonable expectation that Switzerland was a safe place for him to be.

"Roman Polanski would not have decided to go to the film festival in ZÃƒÂƒÃ‚ÂƒÃƒÂ…Ã‚Â’rich in September 2009 if he had not trusted that the journey would not entail any legal disadvantages for him," the Swiss justice ministry said.

Swiss authorities allowed the director to leave prison and stay under house arrest while it considered his extradition. But because Polanski, as a foreign national, was judged a possible flight risk, he had to pay $4.5 million in bail and hand over all of his identification papers to the police.

On Dec. 4, 2009, Polanski was released from his prison cell to begin house arrest at the Milky Way, his three-story chalet in the luxurious resort town of Gstaad, in the Swiss Alps. He was reunited there with his wife and their two children.

Their presence set off a media storm in what is normally a quiet retreat, a winter playground popular with the world's rich and famous. The town has a population of just 2,500 but boasts its own Rolex, Cartier and Hermes outlets. Residents pride themselves on their casual attitude toward celebrities and discretion about their activities.

But the terms of his confinement meant that Polanski could not venture past the boundaries of his property. An electronic anklet monitored his movements, which would alert police in the canton of Bern if he tried to flee or take the anklet off.

He was, however, free to receive visitors. His most recent film, the political thriller "The Ghost Writer," was completed and released during his period of house arrest.